Conventionally, there are chairs each including a body support structure which is formed by a frame member and a membrane having a peripheral edge portion supported by the frame member and which functions as a seat, a backrest, or the like. In this chair, the membrane and the frame member retaining the entire or part of the peripheral edge portion of the membrane form the body support structure so that the membrane forms a body support face. For example, with regard to the seat, a flat seating face is formed by fixing a membrane having a heat shrinkable property to a frame member under no tension or tension lower than tension required of the body support structure and pressing heated aluminum plates against opposite faces of the membrane to heat the membrane and shrink the membrane in front-back and left-right directions to impart the tension for exerting elasticity required of the body support structure (see Patent Literature 1).